If $7a + 4b = 10$ and $3x + 7y = 1$, what is $30x + 12b + 70y + 21a$ ?
Explanation: $= 21a + 12b + 30x + 70y$ $= (3) \cdot (7a + 4b) + (10) \cdot (3x + 7y)$ $= (3) \cdot (10) + (10) \cdot (1)$ $= 30 + 10$ $= 40$